JPH0462336B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrode for detecting acidity and basicity of oil.

[Prior Art] Various types of oils such as fuels, hydraulic oils, quenching oils, and lubricating oils are used in industry, but during storage or use, they undergo oxidation and oxidation in the atmosphere.
Alternatively, it is known that the acidity gradually increases due to accumulation of fuel products, etc., which eventually leads to corrosion and other deterioration in initial performance.

Therefore, rapid and accurate detection of oil deterioration is extremely important in oil management. Conventionally, for this purpose, it has been generally used to know the acidity and basicity of oil based on the petroleum product neutralization value test method specified in JIS K2501. In this method, a certain amount of oil is collected, diluted with a mixed solvent of toluene, isopropyl alcohol, and water prepared separately, and then titrated and analyzed with an acid or base standard solution to determine the amount of acidic and basic components contained in the oil. It is something. However, since this method does not directly detect the acidity or basicity of oil, it is not only complicated to operate, but also has the disadvantage that it cannot continuously detect changes in the acidity or basicity of oil.

On the other hand, an instrument called a PH meter is commercially available as the only device that can directly and continuously detect the acidity and basicity of aqueous solutions with high reliability.
The sensor section of this instrument is based on electrochemical principles and consists of a PH electrode whose electrode potential changes in response to the acidity and basicity of the aqueous solution, and a reference electrode whose electrode potential always remains constant. Ru. When these pairs of electrodes are immersed in the test aqueous solution, the PH
A potential difference proportional to the value is generated, and by measuring this with a potentiometer built into the instrument, the aqueous solution can be measured.
It detects PH, that is, acidity and basicity.

PH electrodes include glass electrodes, antimony electrodes,
Various oxide electrodes are known, while calomel electrodes, variable silver electrodes, and the like are used as reference electrodes. In principle, it is possible to apply a PH meter with such a configuration to detect the acidity and basicity of oil; for example, there has been a proposal to use a commercially available PH meter to detect the basicity of engine oil. (Japanese Unexamined Patent Publication No. 1983-47614).

[Problems with the Prior Art] However, when a commercially available or already known reference electrode is used in oil, there is a problem in that potential stability is significantly lacking due to its structure.

That is, the structure of the above-mentioned known reference electrode is that electrode components containing an aqueous salt solution are generally housed in an outer cylinder made of glass or resin, and a diaphragm having at least a pinhole-sized hole is provided at the end of the outer cylinder. The liquid junction with the test liquid is an essential structure. When a reference electrode with such a structure is used in oil, the aqueous solution inside the outer cylinder comes into contact with the oil through the liquid junction, which not only causes an error in the electrode potential due to the liquid-to-liquid potential difference, but also causes problems over time. At the same time, there was a problem that as a result of mutual diffusion between the internal aqueous solution and the oil, the potential changed greatly from the initial value, and the characteristics as a reference electrode were lost.

Furthermore, the above-mentioned known electrodes have the disadvantage that they cannot be used in a temperature range of 100°C or higher and cannot be applied to, for example, quenching oil having a temperature of 100°C or higher.

The basic purpose of the present invention is to eliminate the above-mentioned drawbacks of known reference electrodes, and in particular, a method for detecting acidity and basicity in oil that does not require an internal solution and can maintain a stable potential in oil, and a method for detecting acidity and basicity in oil. The objective is to provide a reference electrode for this purpose.

[Means and effects for solving the problems] The method for detecting acidity and basicity in oil of the present invention uses an electrode whose electrode potential changes in response to acidity and basicity in oil, and lead and sulfate ions. Using an electrode whose reference potential is the potential based on the equilibrium reaction between and lead sulfate,
It is characterized by measuring potential difference.

The reference electrode for detecting acidity and basicity in oil according to the present invention is characterized in that at least the surface layer that comes into contact with oil is formed by supporting lead sulfate on a base made of metallic lead.

In the present invention, at least the surface layer portion that comes into contact with oil refers to the range of the surface layer portion where the reference electrode of the present invention is expected to be immersed in the test oil in order to detect acidity and basicity in the oil. . In the present invention, the base made of metal lead, when immersed in oil, provides a field for equilibrium reaction between lead and sulfate ions on its surface and lead sulfate, and also transmits the equilibrium potential based on the reaction to an external detection circuit. It serves as a conductor, and at least the surface layer of the base that comes into contact with oil is made of lead metal. Specifically, a rod-shaped, tubular, branch-shaped, or lattice-shaped material in which the core material is made of metallic lead or various metals or non-metallic materials, and the surface layer is coated with metallic lead by plating, cladding, etc., can be used. The purity of the metal lead used in the present invention is preferably as high as possible in order to stabilize the potential when the reference electrode is constructed, but it can be used without any particular problem as long as it has a purity of 99% or more. Lead sulfate (PbSO ₄ ) in the present invention is a crystalline or powdery solid substance, and is a compound that exhibits extremely low solubility in water and oils.

The manufacturing method of the lead sulfate used in the present invention is not particularly limited, but the purity is preferably 99% or higher for the same reason as the above-mentioned lead metal.

Various methods can be used to support the lead sulfate on the substrate, at least the surface layer portion of which comes into contact with oil, which is made of metallic lead. An example of this is as follows.

The first method is to support solid powder of lead sulfate on the substrate using a suitable binder. Specifically, lead sulfate powder is ground to an appropriate particle size using a mortar or the like, then a resin dissolved in a solvent is added to this, and the resulting base is applied to the base in the form of a film. This is a method in which the solvent is then volatilized. The resin used in this method must be selected from a resin that does not dissolve in the oil to which the electrode of the present invention is applied.

The second method is to insert the substrate of the present invention into a cage-shaped or bag-shaped diaphragm made of a plastic film or glass fiber having micropores, and then fill the space between the diaphragm and the substrate with lead sulfate. . Specifically, lead sulfate powder is ground to an appropriate particle size using a mortar or the like, and then water, alcohol, etc. are added to the powder to form a paste, which is then filled and dried. The diaphragm material used in this method needs to be selected from a material that not only does not dissolve in the oil to which the electrode of the present invention is applied, but also does not deteriorate in function, such as softening, at the application temperature.

The third method is to react a metal lead, at least the surface layer that comes into contact with oil, with sulfate ions to generate and support lead sulfate on the surface of the metal lead.

Specifically, the substrate is immersed in an aqueous sulfuric acid solution of about 0.1 to 5N and left as is for a long time, or a DC voltage is applied with the metal lead serving as an anode, and lead sulfate is applied to the surface of the metal lead through electrolytic treatment. A coating layer is formed, and when a desired amount of lead sulfate has been produced, the substrate is pulled up, washed with water, and dried. In this method, lead sulfate is formed as a coating layer of metallic lead, so it has the characteristic of being able to be supported uniformly and with good retention. sex will further improve.
When electrolytic treatment is applied in this method, lead sulfate can be efficiently produced by using a constant potential electrolysis method.

Further, in this supporting method, since a part of the metallic lead is consumed in producing lead sulfate, it is preferable that the substrate is made of sufficiently thick metallic lead. A substrate whose surface layer that comes into contact with oil is made of metallic lead does not necessarily mean that the surface layer is a uniform lead layer, including those in which the surface layer is a lead layer, mesh-shaped lead, or lead wire wound into a coil. It doesn't have to be. Further, as described above, it may be a porous layer of metallic lead.

The material other than lead used for the base body must be conductive, and one that has sufficient durability is selected depending on the conditions of use.

An electrode in which lead sulfate is held on a substrate whose surface layer, at least in contact with oil, is made of lead metal in the manner described above functions as a reference electrode having a constant electrode potential in oil. Although the detailed mechanism by which the electrode of the present invention exhibits a constant electrode potential is unknown, it is thought that the following principle is at work. In other words, although lead sulfate has very little solubility in oil, some of it is ionized,
It is thought that at least the surface layer that comes into contact with the oil is undergoing the following equilibrium reaction on the metal salt substrate.

Pb+SO ₄ ^2- PbSO ₄ +2e (1) Equation (1) The electrochemical equilibrium potential based on the equilibrium reaction of Equation (1), that is, the electrode potential appearing on the conductive substrate, is given by the Nernst equation as follows (T = 25 (℃ constant).

E=E ₀ −0.0296loga SO ^2- ₄ (volts) (2) In equation (2), E ₀ a is the standard electrode potential that indicates a value specific to the reaction, and SO ^2- ₄ is the sulfate ion in oil. It is the activity.

Equation (2) means that the potential appearing on the conductive substrate does not depend on the acidity or basicity of the oil, but changes depending on the activity of the sulfate ion, that is, the ion concentration. However, since lead sulfate is poorly soluble in oil, the concentration of sulfate ions that can exist in oil is extremely low and can be considered to maintain a substantially constant concentration.
In addition, the reaction rate of the equilibrium reaction in equation (1) is extremely high, so even if sulfate ions are mixed in from the outside, they are quickly fixed as lead sulfate, and it is thought that this will not cause a large change in the sulfate ion concentration near the electrode. .

From the above, it can be concluded that the value of E in equation (2) has a virtually constant value at a constant temperature, and that the electrode with lead sulfate supported on metal lead acts as a reference electrode. Thus, in the present invention, it is thought that the action as a reference electrode occurs because at least the surface layer of lead sulfate in oil that comes into contact with oil is formed or exists in the vicinity of the base made of metal lead, and lead sulfate acts as a reference electrode. Even if it is not directly bonded to the metal lead, it only needs to be present in its vicinity, and the term "supported" includes such a state.

In order for the electrode of the present invention to work effectively as a reference electrode, the amount of lead sulfate supported is 1 cm ² on the surface area of the substrate.
A small amount of about 100 μg/cm 2 is sufficient, but taking into account some loss during use of the electrode, a supported amount of 1 to 100 mg/cm ² is preferable.

In addition, the electrode of the present invention is used as a reference electrode, and the PH
When measuring the potential difference between the response electrode and the response electrode, it is necessary to use a potentiometer with as large an input resistance as possible, as in the case of a known reference electrode, and to take care to minimize the flow of current into the circuit. The equilibrium state of equation (1) may be disturbed by the inflow and outflow of minute currents. In order to minimize these adverse effects, the surface area of the conductive substrate should be as large as possible, and specifically, it is preferably 1 to 20 cm ² .

At present, it is difficult to theoretically determine what specific potential the reference electrode of the present invention exhibits in oil, but it is possible to determine it experimentally.

Specifically, the electrode may be combined with a known electrode having a known electrode potential, and the potential difference between the two electrodes may be measured. However, for the purpose of using the reference electrode for detecting the acidity and basicity of oil, it is not necessary to know the absolute value of the potential of the reference electrode, and the potential remains at a constant value without being affected by the acidity and basicity of the test oil. It is sufficient to confirm that the

The electrode of the present invention can be applied to detect the acidity and basicity of oil in the same manner as a conventional PH meter. That is, the reference electrode of the present invention and a PH electrode that responds to acidity and basicity are combined to form a pair of electrodes, and when this electrode pair is immersed in the test oil, the potential difference that appears between the two electrodes is detected with a potentiometer.
The potential difference obtained is proportional to the acidity and basicity of the test oil.

If you create a calibration curve in advance for the relationship between the above potential difference and the acidity and basicity determined by another method, it is possible to directly know the acidity and basicity of the test oil from the detected potential difference. It is. It is also possible to continuously know changes in acidity and basicity of the test oil by detecting changes in potential difference over time. The shape of the conductive substrate used in the reference electrode of the present invention is not particularly limited to the above-mentioned example, and can be appropriately adapted depending on the application, detection conditions, and detection target. Furthermore, the reference electrode of the present invention is temperature stable, not only at room temperature but also at
Can be used at high temperatures above ℃.

Note that there are no particular restrictions on the PH electrode used in pair with the reference electrode of the present invention, and it may be an ordinary glass electrode, an antimony electrode, an electrode whose electrode surface is coated with an oxide, and specifically a Ti-based electrode. TiO ₂ coated electrodes or stainless steel electrodes with passive films can be used. In particular, TiO ₂ electrodes and stainless steel electrodes are preferred electrodes because they have high chemical stability and are robust.

Note that, in general, a small amount of water may be mixed into oil due to moisture absorption or other causes. However, if they are in a compatible state with oil, they will have little effect on the reference electrode of the present invention. in particular,
For example, in the case of lubricating oil for internal combustion engines, the amount of water in the oil is
At about 0.05-1 wt%, the reference electrode is hardly affected. Furthermore, if water is expected to be liberated in oil and become suspended, the amount of metallic lead and lead sulfate constituting the reference electrode of the present invention should be determined by taking into account some elution into free water. It is preferable to have a large amount.

[Examples] Example 1 Lead sulfate as a reagent was thoroughly ground in a mortar, and water was further added to prepare a paste. Next, a lead substrate 1 with a purity of 99.5% and a size of 3×5 cm and a thickness of 2 mm was prepared.
Furthermore, a porous polyethylene sheet with a pore diameter of 0.1 μm and a size of 4 × 10 cm and a thickness of 0.2 mm was prepared, and this was
The diaphragm 2 having a bag-like structure was fabricated by folding it in half to a size of 1 cm and ultrasonically welding the seams at the two long sides. The base 1 is inserted into the inside of this bag-like diaphragm 2.
was inserted, and the paste was further stuffed into the space to form a lead sulfate filling body 3, which was then dried to produce an electrode of the present invention. Figure 4 shows the completed cross-sectional structure.

In order to confirm the performance of the prepared electrode as a reference electrode, potential difference was measured using a saturated calomel electrode, which is a known reference electrode, in a mixed solvent test solution of equal amounts of toluene and 2-propanol. The test solutions were adjusted to various levels of acidity and basicity by adding appropriate amounts of potassium hydroxide and hydrochloric acid.

A potentiometer with an input resistance of 10 ¹¹ Ω was used to measure the potential difference at room temperature. Figure 1 shows the relationship between the potential difference actually measured using a saturated calomel electrode as a reference and the pH of the test solution.

In FIG. 1, the potential difference between the electrode of the present invention and the saturated calomel electrode showed a constant value with fluctuations within 10 mV regardless of the pH of the test solution, and it was confirmed that the potential difference sufficiently satisfied the performance as a reference electrode.

Example 2 A substrate 1 (size: 30 mm x 50 mm) was prepared, which had a core material 1a made of a mild steel plate with a thickness of 1 mm, and a lead coating layer 1b with a purity of 99.5% and a thickness of 1 mm on the surface layer.
This substrate was first washed with a 1N sulfuric acid aqueous solution to remove surface stains. Next, immerse in 1N sulfuric acid aqueous solution,
Furthermore, a lead plate of the same type was placed as a counter electrode and a mercury sulfate electrode was placed as a reference electrode, and anodization was performed for 1 hour at a set potential of -0.43V using a constant potential electrolyzer. Thereafter, the substrate was pulled up, washed with water, and dried. Through these series of steps, a lead sulfate supported electrode having a coating layer 4 of about 1 mg/cm ² of lead sulfate was prepared. The cross-sectional structure of the completed electrode is shown in FIG.

Next, the electrode of the present invention was applied to detect acidity and basicity of engine oil. The test oils were for gasoline engines, and a total of four types of oil were prepared: new oil and three used oils. Size 3 x 5 for acidic and basic response electrodes
An electrode made of SUS310S with a thickness of 1 mm was used.

The two types of electrodes were placed in the test oil so that the distance between the electrodes was 1 mm, the oil temperature was maintained at 80°C, and the potential difference between the two electrodes was measured using the potentiometer used in Example 1.
In addition, the test oil was subjected to titration analysis using the method specified in JIS K2501 to determine the total acid number and total base number.

FIG. 2 shows the relationship between the potential difference and the total acid number actually measured using the electrode of the present invention as a reference, and FIG. 3 shows the relationship between the total base number and the total base number.

In both Figures 2 and 3, the potential difference and the total acid value and total base value show a very valid relationship, and the electrode and method of the present invention are used as reference electrodes for directly detecting the acidity and basicity of oil. It was confirmed that there is something to be satisfied with.

[Effects of the Invention] According to the present invention, a reference electrode is formed based on an equilibrium reaction between lead metal, sulfate ions, and lead sulfate. The reference electrode can be constructed by supporting lead sulfate on a base whose surface layer, at least in contact with oil, is made of lead metal. Since it does not require any internal aqueous solution, which was required with conventional reference electrodes, it can be used as a long-term stable reference electrode for detecting the acidity and basicity of oil even if water is contained in the oil. , temperature constraints are also largely eliminated.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram of the electrode of the present invention based on a saturated calomel electrode, and FIGS. 2 and 3 are characteristic diagrams when the electrode of the present invention is applied to engine oil. Also the fourth
The figure shows a sectional view of the lead sulfate-supported electrode of Example 1, and FIG. 5 shows a sectional view of the lead sulfate-treated electrode of Example 2. 1... Electrode base, 1a... Base core material, 1b...
Lead coating layer, 2...diaphragm, 3...lead sulfate filling body, 4
...Lead sulfate coating layer.

Claims (1)

[Claims] 1. Using an electrode whose electrode potential changes in response to acidity and basicity in oil, and an electrode whose reference potential is the potential based on the equilibrium reaction between lead and sulfate ions and lead sulfate. A method for detecting acidity and basicity in oil, which is characterized by measuring the potential difference. 2 An electrode that is used in combination with an electrode whose electrode potential changes in response to the acidity or basicity of the oil, and whose electrode potential has a certain constant value as a reference, is at least in contact with the oil. A reference electrode for detecting acidity and basicity in oil, characterized by having lead sulfate supported on a base whose surface layer is made of metallic lead.